I expect most people know that the Londonderry Air has been applied to two hymn texts: 'I Cannot Tell' and 'Lord of the Church'. Offhand I think they can be found in Mission Praise. The former would certainly justify its performance at a funeral. In any case I think the tune is pretty good, not least because of the way it lends itself to highly effective and emotional harmonisation.

However it does have a massive range and that open invitation to a drunken rising glissando.
Experience teaches me to transpose most things down for funerals unless there is a large crowd familiar with the hymns..... Slane in D, anyone?